Important: Boiling water concentrates nitrates. Never boil water to make it safer for infants when nitrates may be present in a well water source. This makes the problem worse, not better.

Boiling is the oldest water treatment method in human history. It works reliably for what it’s meant to do. The problem is that most people don’t know what that is.

What Boiling Actually Does

Boiling kills microorganisms. All of them. Bacteria are killed at 70°C (158°F), well below boiling point. Viruses and protozoa including Giardia and Cryptosporidium die at similar temperatures. By the time water reaches a full rolling boil at 100°C (212°F), every recognized waterborne pathogen is dead within seconds.

The EPA and CDC guidance for boil water advisories calls for a rolling boil of 1 minute. At elevations above 6,500 feet, where water boils at a slightly lower temperature, 3 minutes is recommended.

That’s the complete list of what boiling addresses. Biological contamination. Nothing else.

What Boiling Does Not Remove

Lead doesn’t evaporate. It stays in solution. As water boils and some volume is lost to steam, dissolved lead concentrates in the remaining water. Boiling a pot of lead-contaminated water makes the lead concentration slightly higher, not lower.

PFAS compounds are among the most thermally stable molecules in chemistry. The carbon-fluorine bond that makes PFAS so persistent in the environment also makes it resistant to heat. Research has confirmed that boiling has no meaningful effect on PFAS. Don’t boil water to treat PFAS.

Nitrates don’t evaporate. Water does. When you boil a pot of water and lose 20% of the volume to steam, the dissolved nitrates stay in the reduced volume of water. That raises the concentration by 25% or more. This is a known and documented hazard for infants. See the nitrates contaminant page for the full picture.

Fluoride, arsenic, heavy metals generally (mercury, cadmium, chromium-6), dissolved minerals, and hardness compounds don’t leave the water through boiling. Chlorine does reduce somewhat during boiling, because free chlorine is volatile. Chloramines reduce minimally.

The Boil Water Advisory Context

When utilities issue boil water advisories, they’re addressing a specific problem: biological contamination from a system failure. Pressure loss in distribution pipes can allow outside contamination to enter the system. Treatment failures can allow pathogens through. These events produce biological risk.

Boiling addresses exactly what the advisory is about. Follow the advisory exactly as issued.

What boil water advisories are not: a response to lead pipes, PFAS detections, nitrates in source water, or any chemical contamination. If your utility has issued a boil water advisory, it’s about biology. If it’s issued a health advisory about lead or PFAS, the guidance will be different (typically pointing to point-of-use filtration or bottled water).

The Nitrates Problem in More Detail

This is the case where boiling actively causes harm, not just fails to help.

The EPA MCL for nitrates is 10 mg/L. Above that level, nitrates interfere with blood oxygen in infants. Blue baby syndrome (methemoglobinemia) can develop rapidly in infants under 12 months. It can be fatal. See the nitrates page for emergency guidance.

If you’re on a well and you’re not sure of your nitrate level, get it tested before making formula. If you know your well has elevated nitrates and you’re preparing formula, use bottled water or water from a point-of-use RO system. An NSF 58-certified RO removes nitrates.

Do not boil the water. Boiling concentrates nitrates. This is not a nuance. It’s a safety issue.

A Note on the “Boiling Removes Microplastics” Claim

A 2024 study from Chinese researchers found that boiling hard water reduced microplastic concentrations. This was real. It was also specific.

The mechanism: in hard water, calcium and magnesium carbonate precipitate out of solution when heated. The precipitated minerals physically encapsulate some microplastics and settle to the bottom, where they can be removed by pouring through a filter. The researchers used a paper coffee filter to capture the settled material.

This only works in hard water (the study used water with 300+ mg/L hardness). Soft water showed no microplastic reduction from boiling. It also does nothing for PFAS, lead, nitrates, or any dissolved chemical. It’s a narrow finding that doesn’t generalize to water treatment.

When to Boil and When Not To

Boil: when your utility issues a boil water advisory. When you’re camping or in a situation without access to treated water. When flooding has affected your municipal supply and the utility has issued guidance to boil.

Don’t boil: to address lead, PFAS, arsenic, nitrates, or any chemical contamination. Don’t boil for infants when nitrate contamination is possible. Don’t boil as a substitute for a point-of-use filter on a system with known chemical contamination.

For bacteria and biological threats in well water or emergency situations, boiling remains the most reliable and accessible treatment. For chemical contamination, only certified filtration provides documented protection. UV purifiers are another biological treatment option that doesn’t require heat. The full picture of PFAS and nitrate contamination and appropriate treatment is covered in each contaminant’s dedicated guide.